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<title>An improved Version of std::iter_swap</title>
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<div class="titlepage"><div><div><h3 class="title">
<a name="boost_typetraits.examples.iter"></a><a class="link" href="iter.html" title="An improved Version of std::iter_swap">An improved Version of
      std::iter_swap</a>
</h3></div></div></div>
<p>
        Demonstrates a version of <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">iter_swap</span></code>
        that use type traits to determine whether an it's arguments are proxy iterators
        or not, if they're not then it just does a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">swap</span></code>
        of it's dereferenced arguments (the same as <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">iter_swap</span></code>
        does), however if they are proxy iterators then takes special care over the
        swap to ensure that the algorithm works correctly for both proxy iterators,
        and even iterators of different types (see <a href="../../../../examples/iter_swap_example.cpp" target="_top">iter_swap_example.cpp</a>):
      </p>
<pre class="programlisting"><span class="comment">//</span>
<span class="comment">// iter_swap:</span>
<span class="comment">// tests whether iterator is a proxy iterator or not, and</span>
<span class="comment">// uses optimal form accordingly:</span>
<span class="comment">//</span>
<span class="keyword">namespace</span> <span class="identifier">detail</span><span class="special">{</span>

<span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">I</span><span class="special">&gt;</span>
<span class="keyword">static</span> <span class="keyword">void</span> <span class="identifier">do_swap</span><span class="special">(</span><span class="identifier">I</span> <span class="identifier">one</span><span class="special">,</span> <span class="identifier">I</span> <span class="identifier">two</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><a class="link" href="../reference/integral_constant.html" title="integral_constant">false_type</a><span class="special">&amp;)</span>
<span class="special">{</span>
   <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">iterator_traits</span><span class="special">&lt;</span><span class="identifier">I</span><span class="special">&gt;::</span><span class="identifier">value_type</span> <span class="identifier">v_t</span><span class="special">;</span>
   <span class="identifier">v_t</span> <span class="identifier">v</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">one</span><span class="special">;</span>
   <span class="special">*</span><span class="identifier">one</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">two</span><span class="special">;</span>
   <span class="special">*</span><span class="identifier">two</span> <span class="special">=</span> <span class="identifier">v</span><span class="special">;</span>
<span class="special">}</span>
<span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">I</span><span class="special">&gt;</span>
<span class="keyword">static</span> <span class="keyword">void</span> <span class="identifier">do_swap</span><span class="special">(</span><span class="identifier">I</span> <span class="identifier">one</span><span class="special">,</span> <span class="identifier">I</span> <span class="identifier">two</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><a class="link" href="../reference/integral_constant.html" title="integral_constant">true_type</a><span class="special">&amp;)</span>
<span class="special">{</span>
   <span class="keyword">using</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">swap</span><span class="special">;</span>
   <span class="identifier">swap</span><span class="special">(*</span><span class="identifier">one</span><span class="special">,</span> <span class="special">*</span><span class="identifier">two</span><span class="special">);</span>
<span class="special">}</span>

<span class="special">}</span>

<span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">I1</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">I2</span><span class="special">&gt;</span>
<span class="keyword">inline</span> <span class="keyword">void</span> <span class="identifier">iter_swap</span><span class="special">(</span><span class="identifier">I1</span> <span class="identifier">one</span><span class="special">,</span> <span class="identifier">I2</span> <span class="identifier">two</span><span class="special">)</span>
<span class="special">{</span>
   <span class="comment">//</span>
   <span class="comment">// See is both arguments are non-proxying iterators, </span>
   <span class="comment">// and if both iterator the same type:</span>
   <span class="comment">//</span>
   <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">iterator_traits</span><span class="special">&lt;</span><span class="identifier">I1</span><span class="special">&gt;::</span><span class="identifier">reference</span> <span class="identifier">r1_t</span><span class="special">;</span>
   <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">iterator_traits</span><span class="special">&lt;</span><span class="identifier">I2</span><span class="special">&gt;::</span><span class="identifier">reference</span> <span class="identifier">r2_t</span><span class="special">;</span>

   <span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><a class="link" href="../reference/integral_constant.html" title="integral_constant">integral_constant</a><span class="special">&lt;</span><span class="keyword">bool</span><span class="special">,</span>
      <span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><a class="link" href="../reference/is_reference.html" title="is_reference">is_reference</a><span class="special">&lt;</span><span class="identifier">r1_t</span><span class="special">&gt;::</span><span class="identifier">value</span>
      <span class="special">&amp;&amp;</span> <span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><a class="link" href="../reference/is_reference.html" title="is_reference">is_reference</a><span class="special">&lt;</span><span class="identifier">r2_t</span><span class="special">&gt;::</span><span class="identifier">value</span>
      <span class="special">&amp;&amp;</span> <span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><a class="link" href="../reference/is_same.html" title="is_same">is_same</a><span class="special">&lt;</span><span class="identifier">r1_t</span><span class="special">,</span> <span class="identifier">r2_t</span><span class="special">&gt;::</span><span class="identifier">value</span><span class="special">&gt;</span> <span class="identifier">truth_type</span><span class="special">;</span>

   <span class="identifier">detail</span><span class="special">::</span><span class="identifier">do_swap</span><span class="special">(</span><span class="identifier">one</span><span class="special">,</span> <span class="identifier">two</span><span class="special">,</span> <span class="identifier">truth_type</span><span class="special">());</span>
<span class="special">}</span>
</pre>
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